Gfci/light

Hey guys. My friend called me and said he needed a motion light outside his house. He tapped into an existing receptacle in his attic to power the light. This receptacle happened to be part of the the GFCI circuit serving the kitchen countertop outlets. When he first connected the motion light, he said it tripped the circuit breaker and the GFCI receptacle. After turning the power back on he said he was only having trouble with the GFCI tripping.

The circuit breaker tripping tells me that maybe he shorted the hot wire to ground while installing it because it does not trip now. The GFCI tripping i think would mean somewhere the neutral is touching the ground. Everything works normal when he installed a non GFCI receptacle just to test it.

Assuming all wiring is correct and free of contact with other wires, could putting a "motion light" on a GFCI circuit cause the GFCI to trip?